Respiratory waveform analyzer

ABSTRACT

A respiratory waveform analyzer, operable to analyze a respiratory waveform, which is generated based on a temporal change of a concentration of a component in respiratory gas of a subject, includes: a respiratory gas concentration generator which generates a concentration signal based on an output signal from a sensor that is placed to measure the concentration of the component; a flatness calculator which calculates a flatness indicative of flat degree of the respiratory waveform based on a temporal change of the concentration signal; and a reliability calculator which calculates a reliability of the respiratory waveform based on the flatness and the concentration signal.

BACKGROUND OF THE INVENTION

The present invention relates to a respiratory waveform analyzer, andmore particularly to a respiratory waveform analyzer which analyzes therespiratory waveform by detecting the concentration of a component inrespiratory gas of the subject.

Various apparatuses and methods of monitoring the respiration of thepatient who must undergo respiratory management in clinical practice orthe like have been proposed. For example, the method which is calledcapnometry is known as a method in which a temporal change of thepartial pressure of carbon dioxide contained in the expiration or thelike, i.e., the concentration of carbon dioxide (CO₂ concentration) inthe expiration is measured to know the respiratory condition of thepatient (for example, see JP-A-2003-532442).

As a method of measuring the CO₂ concentration in the expiration of thepatient, the photoacoustic spectroscopy, the mass spectroscopy, theRaman scattering spectroscopy, and infrared absorption spectroscopy (IRspectroscopy), and the like are known. Among them, the IR spectroscopyis known as a method in which expiratory gas of the patient isirradiated with light having the carbon dioxide absorption property,such as infrared light, transmitted or reflected light is detected, andthe CO₂ concentration in the expiration is measured from the absorptionrate of the infrared light by the expiratory gas.

In a related-art capnometry, in the waveform of the CO₂ concentration inthe expiration, the maximum value of the waveform corresponding to onerespiration of the patient is set as the effective concentration of therespiration, and detected as an end-tidal carbon dioxide concentration(ETCO2). In the case where the CO₂ concentration in the expiration ismeasured by using the above-described IR spectroscopy, particularly, theproblem is to improve the accuracy of detecting the ETCO2.

When the CO₂ concentration in the expiration is measured by using anexpiratory gas sensor of the mainstream type which is connected to arespiratory circuit to measure the CO₂ concentration, for example, theinspiration of the patient is sometimes humidified. In such a case, itis often that water such as dew condensation water is reserved in therespiratory circuit. When such water is attached to a light irradiationportion or detection portion of the expiratory gas sensor in therespiratory circuit, the CO₂ concentration cannot be correctly detected,with the result that the incorrectly detected concentration appears asnoise components in the measured waveform. Then, it is often that a peakof such noise components is falsely detected as the ETCO2.

In the case where only expirations from the patient with respect to theair supply to the patient by a ventilator are to be counted as therespiratory rate, it is difficult to correctly remove the component ofspontaneous respiration of the patient from the measured waveform.

SUMMARY

It is therefore an object of the invention to provide a respiratorywaveform analyzer which is capable of correctly detecting noisecomponents in a respiratory waveform and analyzing the respiratorywaveform with a high accuracy.

In order to achieve the object, according to the invention, there isprovided a respiratory waveform analyzer, operable to analyze arespiratory waveform, which is generated based on a temporal change of aconcentration of a component in respiratory gas of a subject, therespiratory waveform analyzer comprising:

a respiratory gas concentration generator which generates aconcentration signal based on an output signal from a sensor that isplaced to measure the concentration of the component;

a flatness calculator which calculates a flatness indicative of flatdegree of the respiratory waveform based on a temporal change of theconcentration signal; and

a reliability calculator which calculates a reliability of therespiratory waveform based on the flatness and the concentration signal.

The flatness may be a function of an accumulated value which is obtainedby accumulating degree of a difference in a time interval over aplurality of the time intervals, based on the concentration signal.

The degree of the difference may be an absolute value of the difference.

The degree of the difference may be obtained by raising the differenceto the power of the even number.

The reliability calculator may calculate the reliability based on theflatness which is calculated at a timing by the flatness calculator, andthe concentration signal at the timing.

The respiratory waveform analyzer may further include an effectiveconcentration detector which detects a value of the concentration signalat a timing when the reliability that is calculated in a predeterminedconcentration detecting time period is maximum, as an effectiveconcentration in the concentration detecting time period.

The effective concentration detector may accumulate the reliability inthe concentration detecting time period to obtain an accumulated valuein the concentration detecting time period, and detect the effectiveconcentration in the concentration detecting time period when theaccumulated value exceeds a predetermined reliability.

The concentration detecting time period is a time period correspondingto one cycle of the respiratory waveform.

The respiratory waveform analyzer may further include a weighted averageprocessor which, when a plurality of the effective concentrations aredetected, weights each of the effective concentrations in accordancewith degree of the accumulated value in the corresponding concentrationdetecting time period, and averages the weighted effectiveconcentrations, to calculate a weighted average value.

The respiratory waveform analyzer may further include a display thatdisplays at least one of a number at which the effective concentrationdetector detects the effective concentration in a time period, and theweighted average value calculated by the weighted average processor.

The respiratory gas concentration generator may include: a respiratorygas concentration detector which converts the analog output signal fromthe sensor to a digital respiratory gas signal; and a respiratory gasconcentration calculator which generates a respiratory waveform signalbased on the respiratory gas signal from the respiratory gasconcentration detector. The concentration signal may be the respiratorywaveform signal. When a value of the respiratory gas signal is a valueor greater, which indicates that the concentration of the component ishigh, the effective concentration detector may detect the effectiveconcentration in the concentration detecting time period.

The respiratory waveform analyzer may further include a concentrationdetection value corrector which corrects the respiratory waveform signalcorresponding to the respiratory gas signal, in accordance with a ratioof the respiratory gas signal to a predetermined reference value.

The respiratory waveform analyzer may further include: a respiratoryairway adaptor in which the respiratory gas of the subject flows; and aliquid detector which detects a liquid in the respiratory airwayadaptor.

In order to achieve the object, according to the invention, there isalso provided a respiratory waveform analyzer, operable to analyze arespiratory waveform, which is generated based on a temporal change of aconcentration of a component in respiratory gas of a subject, therespiratory waveform analyzer comprising:

a respiratory gas concentration detector which converts a analog outputsignal from a sensor that is placed to detect the concentration of thecomponent, to a digital respiratory gas signal;

a respiratory gas concentration calculator which generates a respiratorywaveform signal based on the respiratory gas signal from the respiratorygas concentration detector; and

a concentration detection value corrector which corrects the respiratorywaveform signal corresponding to the respiratory gas signal, inaccordance with a ratio of the respiratory gas signal to a predeterminedreference value.

In order to achieve the object, according to the invention, there isalso provided a respiratory waveform analyzer, operable to analyze arespiratory waveform, which is generated based on a temporal change of aconcentration of a component in respiratory gas of a subject, therespiratory waveform analyzer comprising:

a respiratory airway adaptor in which the respiratory gas of the subjectflows, the respiratory airway adaptor provided with a sensor thatmeasures the concentration of the component to output a signal;

a respiratory gas concentration generator which generates aconcentration signal based on the signal output by the sensor, theconcentration signal indicating degree of the concentration; and

a liquid detector which detects a liquid in the respiratory airwayadaptor based on the concentration signal.

The liquid detector may compare a value of the concentration signal withat least one preset value and detect the liquid in the respiratoryairway adaptor based on comparison result.

The sensor may receive a signal light and a referential light which aredifferent from each other in an absorption property of the component,and the liquid detector may calculate attenuance based on receivingintensities of the signal light and the referential light and detect theliquid in the respiratory airway adaptor based on the attenuance.

The liquid detector may output an attention arousing signal when thecomparison result reaches an attention arousal level. The liquiddetector may output an alarm signal when the comparison result reachesan alarm level.

The liquid detector may determine that the comparison result reaches theattention arousal level or the alarm level based on one of a differencebetween the value of the concentration signal and the preset value,number of times at which the value of the concentration signal is largerthan the preset value, a time period during which the value of theconcentration signal is larger than the present value, number of timesat which the value of the concentration signal is smaller than thepreset value and a time period during which the value of theconcentration signal is smaller than the present value.

The liquid detected by the liquid detector may be a water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing the configuration of arespiratory waveform analyzer of an embodiment.

FIG. 2 is an enlarged side view enlargedly showing the vicinity of arespiratory airway adaptor of the respiratory waveform analyzer.

FIG. 3 is a sectional view of the A-A section of FIG. 2 as viewed in thedirection of the arrows in FIG. 2.

FIG. 4 is a functional block diagram showing the configuration of ameasuring device.

FIG. 5 is a view showing an example of a respiratory waveform and theflatness of the respiratory waveform.

FIG. 6 is a view showing an example of a respiratory waveform and thereliability of the respiratory waveform.

FIG. 7 is a view showing a respiratory waveform, the reliability of therespiratory waveform, and an accumulated value of reliabilities duringeach of concentration detecting time periods.

FIG. 8 is a view showing an example of a waveform of a voltage suppliedfrom a respiratory gas concentration detecting portion, and arespiratory waveform which is generated on the basis of the waveform ofthe voltage.

FIG. 9 is a functional block diagram showing the configuration of ameasuring device in another example of the embodiment.

FIG. 10 is a view showing an example of the waveform of the voltagesupplied from the respiratory gas concentration detecting portion, therespiratory waveform which is generated on the basis of the waveform ofthe voltage, and a corrected respiratory waveform, in the measuringdevice.

FIG. 11 is a functional block diagram showing the configuration of ameasuring device in a further example of the embodiment.

FIG. 12 is a view showing an example of a waveform of a voltage(V_(sig)) supplied from the respiratory gas concentration detectingportion, and a respiratory waveform which is generated on the basis ofthe waveform of the voltage, in the measuring device.

FIG. 13 is a view showing an example of the waveform of the voltage(V_(sig)) supplied from the respiratory gas concentration detectingportion, and the respiratory waveform which is generated on the basis ofthe waveform of the voltage, in the measuring device.

FIG. 14 is a view showing an example of the waveform of the voltage(V_(sig)) supplied from the respiratory gas concentration detectingportion, and the respiratory waveform which is generated on the basis ofthe waveform of the voltage, in the measuring device.

FIG. 15 is a view showing an example of the waveform of the voltage(V_(sig)) supplied from the respiratory gas concentration detectingportion, and the respiratory waveform which is generated on the basis ofthe waveform of the voltage, in the measuring device.

FIG. 16 is a view showing relationships between V_(ref) andV_(sig)/V_(ref) due to a change of a CO₂ concentration of therespiration.

FIG. 17 is a view showing an example of waveforms of V_(sig), V_(ref),and a CO₂ concentration which is generated on the basis of V_(sig), in astate where water is not reserved in optical paths of signal light andreferential light inside the respiratory airway adaptor.

FIG. 18 is a view showing relationships between the waveforms of V_(sig)and V_(ref), and the attenuance due to water which is reserved in therespiratory airway adaptor, in the state where water is not reserved inthe optical paths of the signal light and the referential light insidethe respiratory airway adaptor.

FIG. 19 is a view showing an example of waveforms of V_(sig), V_(ref),and a CO₂ concentration which is generated on the basis of V_(sig), in astate where water is reserved in the optical paths of the signal lightand the referential light inside the respiratory airway adaptor.

FIG. 20 is a view showing relationships between the waveforms of V_(sig)and V_(ref), and the attenuance due to water which is reserved in therespiratory airway adaptor, in the state where water is reserved in theoptical paths of the signal light and the referential light inside therespiratory airway adaptor.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, the invention will be described through an embodiment ofthe invention. The invention set forth in the claims is not restrictedby the following embodiment. All of the combinations of the featuresdescribed in the embodiment are not always essential to the solvingmeans of the invention.

FIG. 1 is an exploded perspective view showing the configuration of arespiratory waveform analyzer 10 of the embodiment, FIG. 2 is anenlarged side view enlargedly showing the vicinity of a respiratoryairway adaptor 20 of the respiratory waveform analyzer 10, and FIG. 3 isa sectional view of the A-A section of FIG. 2 as viewed in the directionof the arrows in FIG. 2.

The respiratory waveform analyzer 10 is an apparatus which measures atemporal change of the CO₂ concentration in the expiration of a subjectsuch as a patient who must undergo respiratory management, therebymonitoring the respiratory condition of the subject. The analyzerincludes the respiratory airway adaptor 20, a Y-shaped adaptor 30, aninsertion portion 40, a sensor portion 50, and a measuring device 60.

A respiratory airway 26 through which the respiratory gas of the subjectis to pass is disposed in the respiratory airway adaptor 20. Aconnection port 21 which is connected to a connection port 31 of theY-shaped adaptor 30, and a connection port 22 which is connected to aconnection adaptor 42 of the insertion portion 40 are disposed on theboth ends of the respiratory airway 26, respectively.

A set of sensor attaching faces 24 which are parallel to each other areformed at intermediate positions of the respiratory airway 26 in therespiratory airway adaptor 20, respectively. When the sensor portion 50is attached to the respiratory airway adaptor 20, the sensor attachingfaces 24 are in contact with the inner face of a recess 54 of the sensorportion 50. A transmissive window 25 which is configured by fitting atransmissive member into a circular vacant hole is disposed in each ofthe sensor attaching faces 24. The transmissive windows 25 are disposedat positions which correspond to openings 56 in the inner face of therecess 54 when the sensor portion 50 is attached, respectively.

The Y-shaped adaptor 30 has: the connection port 31 which is connectedto the connection port 21 of the respiratory airway adaptor 20; aninspiratory air pipe 32 which is to be connected to an air supply sourceside of a ventilator; and an expiration air pipe 33 which is to beconnected to an expiratory discharge valve side of the ventilator. TheY-shaped adaptor 30 is a member through which air that is supplied from,for example, the ventilator to the subject passes, and the expirationfrom the subject passes to the expiratory discharge valve side of theventilator.

The insertion portion 40 has a tube 41 which is to be inserted into theairway of the subject, and a connection adaptor 42 which mediatesconnection between one end of the tube 41 and the connection port 22 ofthe respiratory airway adaptor 20.

The sensor portion 50 has: a sensor housing portion 51 which has asubstantially U-like shape, and in which a light emitter 52 that emitsinfrared light, and a light receiver 53 that receives the infrared lightfrom the light emitter 52, and that outputs a voltage the level of whichcorresponds to the intensity of the received light are disposed; and aconnection cable 55 through which the sensor housing portion 51 isconnected to the body unit 61 of the measuring device 60. As shown inFIGS. 1 and 3, the light emitter 52 and the light receiver 53 areopposed to each other across the recess 54 formed in the sensor housingportion 51.

As shown in FIGS. 2 and 3, the circular openings 56 are disposed at thepositions where the light emitter 52 and the light receiver 53 aredisposed, in the inner face of the recess 54. As shown in FIG. 3, thelight emitter 52 is electrically connected through wirings 52 a, 52 b,and the light receiver 53 is electrically connected through wirings 53a, 53 b to the body unit 61 of the measuring device 60.

In the embodiment, the light emitter 52 emits infrared light inaccordance with the electric power supplied from the body unit 61. Asthe light emitter 52, a device for emitting light of a wavelength atwhich the rate of absorption by CO₂ gas is higher as compared with thelonger and shorter wavelength sides is used. When receiving the lightfrom the light emitter 52, therefore, the light receiver 53 outputs avoltage the level of which is substantially proportional to the CO₂concentration. The light emitter 52 is a single light source emittinglight having a large band and the light receiver 53 narrows the band byusing a filter when receiving the light.

The measuring device 60 has the body unit 61 which is connected to thesensor housing portion 51 of the sensor portion 50 through a connectioncable 55, and a displaying portion 62 and operating portion 63 which aredisposed in the front face of the body unit 61.

In a state where the respiratory airway adaptor 20, the Y-shaped adaptor30, and the insertion portion 40 are assembled together, and the sensorportion 50 is attached to the respiratory airway adaptor 20, therespiratory waveform analyzer 10 is used for measuring the concentrationof carbon dioxide (CO₂ concentration) in the expiration or inspiration(hereinafter, both are generally referred as “respiration”) of thesubject.

In the measurement by the respiratory waveform analyzer 10, therespiration of the subject which passes through the respiratory airway26 of the respiratory airway adaptor 20 is irradiated with the infraredlight which is emitted from the light emitter 52 in accordance with theelectric power supplied from the measuring device 60, and transmittedlight is received by the light receiver 53. Then, the light receiver 53outputs a voltage the level of which corresponds to the intensity of thereceived light, to the measuring device 60.

Based on the voltage from the light receiver 53, the measuring device 60detects the partial pressure of carbon dioxide in the pressure of therespiration which passes through the respiratory airway 26. The partialpressure of carbon dioxide has a value corresponding to theconcentration of CO₂ contained in the respiration which passes throughthe respiratory airway 26. In the following description, therefore, thepartial pressure of carbon dioxide detected by the measuring device 60is referred to as the CO₂ concentration.

The measuring device 60 generates a waveform based on a temporal changeof the detected CO₂ concentration, and displays the waveform on thedisplaying portion 62. In the following description, the waveform isreferred to as the respiratory waveform. Various measurement conditionsin the measurement, a change of the manner of displaying the respiratorywaveform on the displaying portion 62, and the like can be set aspredetermined ones by operating the operating portion 63 of themeasuring device 60.

Hereinafter, the detection of the CO₂ concentration by the measuringdevice 60, and generation and analysis of the respiratory waveform willbe described in more detail.

FIG. 4 is a functional block diagram showing the configuration of themeasuring device 60. The illustration of the configuration related tothe power supply to the light emitter 52 is omitted (the same shallapply to the other functional block diagrams). As shown in FIG. 4, themeasuring device 60 has a respiratory gas concentration detectingportion 100 and a calculating processing portion 200, in the body unit61. The calculating processing portion 200 includes a respiratory gasconcentration calculating portion 210, a flatness calculating portion220, a reliability calculating portion 230, a respiratory rate detectingportion 240, an effective concentration detecting portion 250, and aweighted average processing portion 260.

When receiving an analog output signal which is supplied in, forexample, a time continuous manner from the sensor portion 50, therespiratory gas concentration detecting portion 100 converts the analogsignal to a digital respiratory gas signal which corresponds to thelevel of the analog signal, and supplies the digital signal to therespiratory gas concentration calculating portion 210 and the effectiveconcentration detecting portion 250. The respiratory gas concentrationdetecting portion 100 is configured by an A/D converter and the like.The respiratory gas concentration detecting portion 100 and therespiratory gas concentration calculating portion 210 correspond to therespiratory gas concentration generating portion in the invention.

The respiratory gas concentration calculating portion 210 receives thevoltage (respiratory gas signal) of a level which corresponds to the CO₂concentration supplied from the respiratory gas concentration detectingportion 100, and generates the respiratory waveform. The respiratory gasconcentration calculating portion 210 supplies the generated respiratorywaveform to the displaying portion 62, the flatness calculating portion220, the reliability calculating portion 230, the respiratory ratedetecting portion 240, and the effective concentration detecting portion250.

The flatness calculating portion 220 calculates the flatness indicativeof the flat degree of the respiratory waveform supplied from therespiratory gas concentration calculating portion 210. The flatnesscalculating portion 220 calculates the difference between previous andcurrent CO₂ concentrations at specific time intervals, and thencalculates the flatness based on degree of the difference. The degree ofthe difference may be an absolute value of the difference and may beobtained by raising the difference to the power of the even number.Specifically, the flatness calculating portion 220 calculates theflatness by using the following calculation expression (Exp. 1). Theflatness calculating portion 220 sequentially outputs the calculatedflatness in a time series manner to the reliability calculating portion230.Y[0]=1/{Σ(DΔtCO2)²+1}  [Exp. 1]

Y[0]: current flatness in the respiratory waveform

DΔtCO2: difference between previous and current CO₂ concentrations attime interval Δt

In Exp. 1 above, the time interval Δt may be, for example, 0.05 seconds,and Σ(DΔtCO2)² may be, for example, an accumulated value of the squaresof the differences which are calculated during 0.1 seconds immediatelybefore the calculation of the flatness. As indicated by Exp. 1 above,the flatness calculated by the flatness calculating portion 220 is afunction of the accumulated value of the squares of the differences, andhas the maximum value when the accumulated value is minimum.

FIG. 5 shows an example of the respiratory waveform and the flatness ofthe respiratory waveform. In the respiratory waveform shown in FIG. 5,the flatness is reduced in portions (the vicinities of 5 and 15 secondsin FIG. 5) where the temporal change of the CO₂ concentration is violentdue to, for example, adhesion of water droplets to the transmissivewindows 25 of the respiratory airway adaptor 20, and those (thevicinities of 9 and 20 seconds in FIG. 5) where the CO₂ concentration isvaried due to spontaneous respiration of the subject or the like.

The reliability calculating portion 230 calculates the reliability ofthe respiratory waveform on the basis of the degree of the flatnesssupplied from the flatness calculating portion 220, and the respiratorywaveform supplied from the respiratory gas concentration calculatingportion 210. Specifically, the reliability calculating portion 230calculates, as the reliability, a value in which the flatness calculatedby the flatness calculating portion 220 is multiplied with the value(the degree of the CO₂ concentration) of the respiratory waveformcorresponding to the timing of calculating the flatness. Then, thereliability calculating portion 230 sequentially outputs the calculatedreliability in a time series manner to the respiratory rate detectingportion 240, the effective concentration detecting portion 250, and theweighted average processing portion 260.

FIG. 6 shows an example of the respiratory waveform and the reliabilityof the respiratory waveform. As shown in FIG. 6, at a timing when theflatness corresponding to the respiratory waveform is reduced, thereliability of the respiratory waveform shows a tendency to reduceirrespective of the degree of the CO₂ concentration. Namely, thereliability shows a reduction tendency when the respiratory waveform islargely varied in a short time period because, for example, waterdroplets adhere to the transmissive windows 25 of the respiratory airwayadaptor 20, or the subject performs spontaneous respiration.

The effective concentration detecting portion 250 detects the timeperiod corresponding to one cycle from the respiratory waveform suppliedfrom the respiratory gas concentration calculating portion 210. In theembodiment, the effective concentration detecting portion 250 detects aportion of the respiratory waveform, extending from a timing when theCO₂ concentration exceeds a predetermined threshold (C_(th)) to thatwhen the CO₂ concentration again falls below the threshold, as anexpiratory waveform in one cycle of the respiratory waveform. In therespiratory waveform shown in FIG. 6, for example, the effectiveconcentration detecting portion 250 detects eight expiratory waveforms(W₁ to W₈).

The effective concentration detecting portion 250 detects time periodsrespectively corresponding to the expiratory waveforms, as concentrationdetecting time periods (T₁ to T₈) in the expiratory waveforms. As shownin FIG. 6, for example, the effective concentration detecting portion250 detects the concentration detecting concentration detecting timeperiods (T₁ to T₈) for the eight expiratory waveforms (W₁ to W₈),respectively.

The effective concentration detecting portion 250 extracts reliabilitiesin the respective concentration detecting time periods, and detectstimings when the value of the reliability is maximum. As shown in FIG.6, for example, the effective concentration detecting portion 250extracts the reliabilities (R₁ to R₈) in the respective concentrationdetecting time periods (T₁ to T₈), and detects the timings (P₁ to P₈)when the value of the reliability is maximum in each of theconcentration detecting time periods.

The effective concentration detecting portion 250 detects the value (CO₂concentration) of the expiratory waveform at the timing when thereliability is maximum in each of the concentration detecting timeperiods, as the effective concentration in the expiratory waveform. Asshown in FIG. 6, for example, the effective concentration detectingportion 250 detects the CO₂ concentrations at the timings (P₁ to P₈)which are detected in the respective concentration detecting timeperiods (T₁ to T₈), as the effective concentrations in the correspondingexpiratory waveforms (W₁ to W₈), respectively.

At a timing when the respiratory waveform is largely varied, thereliability is reduced as described above, and hence the effectiveconcentration detecting portion 250 does not detect the CO₂concentration at the timing as the effective concentration.

As described above, the respiratory waveform analyzer 10 of theembodiment can correctly know noise components in the respiratorywaveform on the basis of the reliability calculated by the reliabilitycalculating portion 230. Even in the case where the respiratory waveformis largely varied due to, for example, adhesion of water droplets to thetransmissive windows 25 of the respiratory airway adaptor 20, when thereliability is used, a peak of the varying portion is not detected asthe effective concentration, and the effective CO₂ concentration in eachcycle of the respiratory waveform can be detected with a higheraccuracy.

FIG. 7 shows a respiratory waveform, the reliability of the respiratorywaveform, and the accumulated value of reliabilities during each ofconcentration detecting time periods. The respiratory waveform andreliability of the respiratory waveform which are shown in FIG. 7 areidentical with those shown in FIG. 6. Therefore, the expiratorywaveforms (W₁ to W₈), concentration detecting time periods (T₁ to T₈),and the like which are denoted by the same reference numerals as thoseof FIG. 6 are identical with those shown in FIG. 6, and hence theirdescription is omitted.

In the embodiment, the effective concentration detecting portion 250accumulates the reliabilities in the respective concentration detectingtime periods, and compares the value of the accumulation with apredetermined lower-limit reliability. Then, the effective concentrationdetecting portion 250 detects the effective concentration, only inconcentration detecting time periods when the accumulated value exceedsthe lower-limit reliability.

The detection will be described more specifically with reference to therespiratory waveform shown in FIG. 7. The effective concentrationdetecting portion 250 accumulates the reliabilities in each of theconcentration detecting time periods (T₁ to T₈), to calculateaccumulated values (S₁ to S₈) respectively corresponding to theconcentration detecting time periods. In the effective concentrationdetecting portion 250, for example, a value which is larger than theaccumulated values (S₃, S₆) of the reliabilities corresponding to theexpiratory waveforms (W₃, W₆) generated by spontaneous respiration ofthe subject, and which is smaller than any of the accumulated values(S₁, S₂, S₄, S₅, S₇, S₈) of the reliabilities corresponding to thenormal expiratory waveforms (W₁, W₂, W₄, W₅, W₇, W₈) with respect to theair supply from the ventilator is stored as the lower-limit reliability.

Then, the effective concentration detecting portion 250 calculates theaccumulated values (S₁ to S₈) of the reliabilities in the respectiveconcentration detecting time periods (T₁ to T₈), and compares theaccumulated values with the lower-limit reliability. The effectiveconcentration detecting portion 250 detects the effective concentrationin only the concentration detecting time periods (T₁, T₂, T₄, T₅, T₇,T₈) corresponding to, among the accumulated values, the accumulatedvalues (S₁, S₂, S₄, S₅, S₇, S₈) which are larger than the lower-limitreliability. The effective concentration detecting portion 250 suppliesthe detected effective concentrations (hereinafter, indicated by C₁, C₂,C₄, C₅, C₇, C₈) to the weighted average processing portion 260 and thedisplaying portion 62. The displaying portion 62 displays the effectiveconcentrations.

In the respiratory waveform analyzer 10 of the embodiment, as describedabove, the effective concentration detecting portion 250 does not detectthe effective concentration with respect to an expiratory waveform whichis generated by, for example, spontaneous respiration of the subject,and which has a low reliability, and therefore can detect the effectiveCO₂ concentration with respect to only normal expiration from thesubject for the air supply from the ventilator.

The respiratory rate detecting portion 240 detects the respiratory rateper unit time period, on the basis of the respiratory waveform suppliedfrom the respiratory gas concentration calculating portion 210 and thereliability supplied from the reliability calculating portion 230.Similarly with the effective concentration detecting portion 250,specifically, the respiratory rate detecting portion 240 detects, forexample, a portion of the respiratory waveform, extending from a timingwhen the CO₂ concentration exceeds a predetermined threshold to thatwhen the CO₂ concentration again falls below the threshold, as anexpiratory waveform in one cycle of the respiratory waveform.

Then, the respiratory rate detecting portion 240 calculates theaccumulated values of the reliabilities supplied from the reliabilitycalculating portion 230, and, similarly with the effective concentrationdetecting portion 250, compares the accumulated values with thelower-limit reliability. With respect to only expiratory waveformscorresponding to, among the accumulated values, accumulated values whichexceed the lower-limit reliability, then, the respiratory rate detectingportion 240 detects the respiratory rate of the subject per unit timeperiod, and supplies numerical data of the respiratory rate to thedisplaying portion 62. The displaying portion 62 displays therespiratory rate of the subject per unit time period.

In the embodiment, as described above, the respiratory rate is notcounted with respect to an expiratory waveform which is generated by,for example, spontaneous respiration of the subject, and which has a lowreliability. Therefore, the respiratory rate based on the respiratorymotion of the subject with respect to the air supply from the ventilatorcan be detected more correctly.

In the case where the plurality of effective concentrations are detectedfrom the respiratory waveform in the effective concentration detectingportion 250, the weighted average processing portion 260 calculates aweighted average value in which the effective concentrations areweighted respectively in accordance with the degrees of accumulatedvalues of the reliabilities corresponding to the effectiveconcentrations, and then averaged.

In the respiratory waveform shown in FIG. 7, for example, the weightedaverage processing portion 260 calculates a weighted average value onthe basis of the following calculation expression (Exp. 2), from theeffective concentrations (C₁, C₂, C₄, C₅, C₇, C₈) which are detectedfrom the expiratory waveforms W₁, W₂, W₄, W₅, W₇, W₈ by the effectiveconcentration detecting portion 250, and the accumulated values (S₁, S₂,S₄, S₅, S₇, S₈) of the reliabilities respectively corresponding to thecorrect expiratory waveforms. Then, the weighted average processingportion 260 supplies the calculated weighted average value to thedisplaying portion 62. The displaying portion 62 displays the weightedaverage value.AV=(C1×S1+C2×S2+C4×S4+C5×S5+C7×S7+C8×S8)/(S1+S2+S4+S5+S7+S8)  [Exp. 2]

AV: weighted average value

Furthermore, the weighted average processing portion 260 may update theweighted average value in accordance with that the effectiveconcentration detecting portion 250 newly detects the effectiveconcentration on the basis of the respiratory waveform. For example, theweighted average processing portion 260 may update the weighted averagevalue, at constant time intervals in accordance with the new effectiveconcentration which is detected by the effective concentration detectingportion 250, and the degree of the accumulated value of reliabilitiescorresponding to the effective concentration.

In the respiratory waveform analyzer 10 of the embodiment, as describedabove, a weighted average value is calculated in which the effectiveconcentrations detected from the respiratory waveform are weighted andaveraged in accordance with accumulated values of the reliabilities ofthe respiratory waveform. Therefore, the detected effectiveconcentrations are displayed as they are on the displaying portion 62,and also can be displayed as the average value in which the effectiveconcentrations calculated from the expiratory waveform having low noisecomponents are more reflected.

FIG. 8 shows an example of a waveform of the voltage (V_(sig)) suppliedfrom the respiratory gas concentration detecting portion 100, and arespiratory waveform which is generated on the basis of the waveform ofthe voltage. In the respiratory waveform shown in FIG. 8, similarly withthat shown in FIG. 6, waveforms of W₁₁ to W₁₃ are respiratory waveformswhich are detected by the effective concentration detecting portion 250on the basis of comparison with the predetermined threshold (C_(th)). Inthe figure, T₁₁ to T₁₃ indicate concentration detecting time periods forthe expiratory waveforms (W₁₁ to W₁₃), respectively.

In a use of the respiratory waveform analyzer 10, when the intensity ofthe received light in the light receiver 53 of the sensor portion 50 islowered by, for example, adhesion of water droplets to the transmissivewindows 25 of the respiratory airway adaptor 20, also the value of thevoltage supplied from the light receiver 53 is lowered in accordancewith the lowering of the intensity. At this time, the respiratorywaveform which is generated by the respiratory gas concentrationcalculating portion 210 is sometimes abruptly varied irrespective of theactual degree of the concentration of CO₂ contained in the respirationwhich passes through the respiratory airway 26.

In the measuring device 60, by contrast, the effective concentrationdetecting portion 250 receives the voltage (V_(sig)) supplied from therespiratory gas concentration detecting portion 100, and compares thevoltage with a preset lower-limit voltage. Then, the effectiveconcentration detecting portion 250 removes time periods in which thevalue of the voltage (V_(sig)) is smaller than the lower-limit voltage(V_(th)), from the concentration detecting time periods for therespiratory waveform. In the respiratory waveform shown in FIG. 8, forexample, the effective concentration detecting portion 250 detects theeffective concentration in time periods that are obtained by removingtime periods (T_(D1) to T_(D3)) in which the value of the voltage(V_(sig)) is smaller than the lower-limit voltage (V_(th)) from theconcentration detecting time periods (T₁₁ to T₁₃) for the expiratorywaveforms (W₁₁ to W₁₃).

In the respiratory waveform analyzer 10 of the embodiment, as describedabove, the effective concentration is detected after noise components inthe respiratory waveform are removed, and hence the effectiveconcentration of CO₂ contained in the respiration of the subject can bedetected more correctly.

FIG. 9 is a functional block diagram showing the configuration of ameasuring device 65 in another example of the embodiment. In themeasuring device 65, components similar to those of the measuring device60 which has been described with reference to FIG. 4 are denoted by thesame reference numerals, and their description is omitted.

The measuring device 65 has the respiratory gas concentration detectingportion 100 and a calculating processing portion 201, in the body unit61. The calculating processing portion 201 includes a concentrationdetection value correcting portion 270 in addition to the componentswhich are included by the calculating processing portion 200.

The concentration detection value correcting portion 270 receives thevoltage supplied from the respiratory gas concentration detectingportion 100, and corrects the respiratory waveform in accordance withthe ratio of the voltage value to a predetermined reference voltagevalue. Specifically, the concentration detection value correctingportion 270 calculates a correction value in which the CO₂ concentrationcorresponding to the voltage value in the respiratory waveform iscorrected on the basis of, for example, the following calculationexpression (Exp. 3), and outputs a time series of the correction valueas a corrected respiratory waveform to the displaying portion 62 and therespiratory rate detecting portion 240. The displaying portion 62displays the corrected respiratory waveform.F_CO2[0]=a(Vsig/Vsig0)^(b) ×Cp+[1−a(Vsig/Vsig0)^(b) ]×F_CO2[1]  [Exp. 3]

F_CO2[0]: correction value of the CO₂ concentration

F_CO2[1]: CO₂ concentration at the previous timing

Cp: current CO₂ concentration

Vsig: current voltage value

Vsig0: reference voltage value

a: weighting adjustment factor

b: weighting adjustment factor

In Exp. 3 above, the reference voltage value (Vsig0) is a voltage valuewhich is supplied from the respiratory gas concentration detectingportion 100 when the measurement is performed by the respiratorywaveform analyzer 10 in a state where no gas exists in the respiratoryairway 26 of the respiratory airway adaptor 20.

The weighting adjustment factors (a, b) are factors for adjusting thecorrection value to a value in which the ratio (Vsig/Vsig0) of a changeof the current voltage value (the voltage value to be corrected) to thereference voltage value is more reflected to the current CO₂concentration (Cp), or that in which the ratio is more reflected to theCO₂ concentration (F_CO2[1]) at the previous timing. In the embodiment,preferably, a is a value in the range of 0 to 1, and b is a value whichis equal to or larger than 0.

FIG. 10 shows an example of the waveform of the voltage (V_(sig))supplied from the respiratory gas concentration detecting portion 100,the respiratory waveform which is generated on the basis of the waveformof the voltage, and a corrected respiratory waveform, in the measuringdevice 65. The waveform indicated by “CO₂ CONCENTRATION” in FIG. 10 isthe respiratory waveform which is generated by the respiratory gasconcentration calculating portion 210 on the basis of the voltage(V_(sig)) supplied from the respiratory gas concentration detectingportion 100, and the waveform indicated by “CORRECTED CO₂ CONCENTRATION”in FIG. 10 is the respiratory waveform which is obtained by correctingthe waveform indicated by “CO₂ CONCENTRATION”, in accordance with thecalculation expression of Exp. 3 above by the concentration detectionvalue correcting portion 270.

In the example, both the weighting adjustment factors (a, b) in Exp. 3above are set to 1. In the example, therefore, the concentrationdetection value correcting portion 270 calculates the correction value(F_CO2[0]) in which, as the ratio of the voltage (V_(sig)) supplied fromthe respiratory gas concentration detecting portion 100 to the referencevoltage value (V_(sig0)) is smaller, the CO₂ concentration (Cp)generated by the respiratory gas concentration calculating portion 210on the basis of the voltage (V_(sig)) is made smaller in accordance withthe ratio.

Even when the voltage (V_(sig)) is made to a small value in which theCO₂ concentration of the respiration that passes through the respiratoryairway 26 is not reflected, by the lowering of the intensity of thereceived light in the light receiver 53 due to a measurement error causesuch as adhesion of water droplets to the transmissive windows 25 of therespiratory airway adaptor 20, therefore, the concentration detectionvalue correcting portion 270 can generate a respiratory waveform inwhich an abrupt change of the CO₂ concentration (Cp) due to themeasurement error cause is mitigated.

Furthermore, the respiratory rate detecting portion 240 can detect morecorrectly the respiratory rate of the subject per unit time period, andthe displaying portion 62 can display a respiratory waveform which isless affected by the measurement error cause, and which is more similarto the CO₂ concentration of the respiration of the subject.

Water which is generated in the respiratory circuit during the use ofthe respiratory waveform analyzer 10 of the embodiment constitutes notonly the error cause of the measurement of the CO₂ concentration asdescribed above, but also may constitute a cause of pneumonia when thepatient erroneously sucks the water. Therefore, the generation of watermust be detected more correctly. Hereinafter, the respiratory waveformanalyzer 10 which can solve such a problem will be exemplarilydescribed.

FIG. 11 is a functional block diagram showing the configuration of ameasuring device 66 in a further example of the embodiment. FIGS. 12 to15 show examples of a waveform of the voltage (V_(sig)) supplied fromthe respiratory gas concentration detecting portion 100, and arespiratory waveform which is generated on the basis of the waveform ofthe voltage, in the measuring device 66.

In the measuring device 66 shown in FIG. 11, components similar to thoseof the measuring device 60 which has been described with reference toFIG. 4 or those of the measuring device 65 which has been described withreference to FIG. 9 are denoted by the same reference numerals, andtheir description is omitted. The waveforms indicated by “CO₂CONCENTRATION” in FIGS. 12 to 15 are the respiratory waveform which isgenerated by the respiratory gas concentration calculating portion 210on the basis of the voltage (V_(sig)) supplied from the respiratory gasconcentration detecting portion 100.

The measuring device 66 has the respiratory gas concentration detectingportion 100 and a calculating processing portion 202, in the body unit61. The calculating processing portion 202 includes a reserved waterdetecting portion 280 in addition to the components which are includedby the calculating processing portion 200.

The reserved water detecting portion 280 receives the voltage (V_(sig))supplied from the respiratory gas concentration detecting portion 100,and compares the value of the voltage (V_(sig)) with a preset attentionarousing voltage (V_(ALM1)). In the example, the attention arousingvoltage (V_(ALM1)) is set to a level at which the voltage (V_(sig)) ishigher than the attention arousing voltage (V_(ALM1)) in the case where,in the use of the respiratory waveform analyzer 10, the measurement isperformed without causing water to adhere to the transmissive windows 25of the respiratory airway adaptor 20.

When, in the use of the respiratory waveform analyzer 10, water reservedin the respiratory airway adaptor 20 adheres to the transmissive windows25 of the respiratory airway adaptor 20, the intensity of light receivedby the light receiver 53 of the sensor portion 50 is lowered. When thevoltage (V_(sig)) is lowered in accordance with the lowering of theintensity of the light received by the light receiver 53, to be lowerthan the attention arousing voltage (V_(ALM1)) as shown in FIG. 12, thereserved water detecting portion 280 supplies an attention arousingsignal indicative of a possibility that water is reserved in therespiratory airway adaptor 20, to the displaying portion 62. Uponreceiving the attention arousing signal, the displaying portion 62displays for a constant time period (T_(ALM1)) an attention arousingmessage indicating that water may be possibly reserved in therespiratory airway adaptor 20, based on the attention arousing signal.

When the voltage (V_(sig)) is lowered to be lower than the attentionarousing voltage (V_(ALM1)), the reserved water detecting portion 280compares the value of the voltage (V_(sig)) with a preset alarm voltage(V_(ALM2)). In the example, the alarm voltage (V_(ALM2)) is set to alevel at which the voltage (V_(sig)) is lower than the alarm voltage(V_(ALM2)) in the case where, in the use of the respiratory waveformanalyzer 10, the measurement is performed in a state where water adheresto a substantially whole face of the transmissive windows 25 of therespiratory airway adaptor 20.

When the voltage (V_(sig)) is further lowered to be lower than the alarmvoltage (V_(ALM2)) as shown in FIG. 13, the reserved water detectingportion 280 supplies an alarm signal indicating that water is reservedin the respiratory airway adaptor 20, to the displaying portion 62. Uponreceiving the alarm signal, the displaying portion 62 displays for aconstant time period (T_(ALM2)) an alarm message indicating, forexample, that water is reserved in the respiratory airway adaptor 20,based on the alarm signal.

Furthermore, the reserved water detecting portion 280 may accumulate thenumber at which the value of the voltage (V_(sig)) is smaller than thepreset attention arousing voltage (V_(ALM1)) as shown in FIG. 14, foreach respiratory waveform, and, at a timing when the number of smallervalues reaches a preset number (in FIG. 14, three), supply the attentionarousing signal to the displaying portion 62. Moreover, the reservedwater detecting portion 280 may count the number at which the value ofthe voltage (V_(sig)) is smaller than the attention arousing voltage(V_(ALM1)), and, at a timing when the counted number reaches a presetnumber (in FIG. 14, eight) which is a number larger than theabove-mentioned number, supply the alarm signal to the displayingportion 62.

Furthermore, the reserved water detecting portion 280 may accumulate thetime period during which the value of the voltage (V_(sig)) is smallerthan the preset attention arousing voltage (V_(ALM1)) as shown in FIG.15, and, at a timing when the accumulated time period reaches a presettime period, supply the attention arousing signal to the displayingportion 62. Moreover, the reserved water detecting portion 280 mayaccumulate the time period during which the value of the voltage(V_(sig)) is smaller than the preset alarm voltage (V_(ALM2)) as shownin FIG. 15, and, at a timing when the accumulated time period reaches apreset time period, supply the alarm signal to the displaying portion62.

As described above, the respiratory waveform analyzer 10 of theembodiment further includes the reserved water detecting portion 280,and hence can detect that water is reserved in the respiratory airwayadaptor 20, to perform an attention arousal and an alarm to the user ofthe apparatus. In the example, the attention arousal and alarm relatedto reserving of water in the respiratory airway adaptor 20 are performedby means of a message display on the displaying portion 62.Alternatively, the attention arousal and the alarm may be performed bymeans of, for example, a buzzer or an audio assist.

In the above-described embodiment example of the respiratory waveformanalyzer 10, the light emitter 52 emits light (signal light) of a bandin which the rate of absorption by CO₂ gas is high, and the lightreceiver 53 receives the light which has undergone absorption inaccordance with the concentration of CO₂ contained in the respiration.Hereinafter, an embodiment example in which the light emitter 52 emitsalso light (referential light) of a band in which the rate of absorptionby CO₂ gas is low, in addition to the signal light will be described.The respiratory waveform analyzer 10 which will be described below has aconfiguration similar to that of the respiratory waveform analyzer 10 ofthe above-described embodiment example.

In the example, the light emitter 52 alternately emits the signal lightand the referential light. The respiratory gas concentration detectingportion 100 outputs voltages of levels which correspond to the receivingintensities of the signal light and the referential light, respectively.In the example, namely, the respiratory gas concentration detectingportion 100 outputs the voltage (V_(sig)) of a level which correspondsto the receiving intensity of the signal light, and also a voltage(V_(ref)) of a level which corresponds to the receiving intensity of thereferential light. Since the referential light is not substantiallyabsorbed by CO₂ as compared with the signal light, the value of thevoltage (V_(ref)) is changed by increasing and decreasing of theconcentration of CO₂ contained in the respiration, in a less degree ascompared with the voltage (V_(sig)). In order to alternately emit thesignal light and the referential light, a plurality of light sources foremitting light may be provided respectively as the light emitter 52. Inaddition, the configuration may be used in which a single light sourcefor emitting light having a large band is provided as the light emitter52, the light from the single light source is divided at the lightreceiver 53 and the signal light and the referential light are generatedby using filters, which have different characteristics, for filteringthe divided light.

With respect to the receiving intensity of the referential light, thefollowing expression holds in accordance with the Lambert-Beer Law.ref/ref0=e ^(−ECD)  [Exp. 4]

In expression (Exp. 4) above, ref indicates the receiving intensity ofthe referential light, and ref0 indicates the receiving intensity of thereferential light (standard referential light) in a state where no wateris reserved in the respiratory airway adaptor 20. Furthermore, Eindicates the absorption coefficient, C indicates the concentration ofwater existing in the optical path of the referential light, and Dindicates the thickness of the water in the direction of the opticalpath. Moreover, above expression (Exp. 4) can be transformed in thefollowing manner.ECD=−ln(ref/ref0)  [Exp. 5]

In the expression, the absorption coefficient (E) of the water reservedin the respiratory airway adaptor 20, and the concentration (C) of thewater can be regarded as constants, and hence above expression (Exp. 5)is an expression showing the relationship between the quantity of waterreserved in the respiratory airway adaptor 20 and the degree ofattenuation of the referential light caused by the water (the attenuancedue to water). When the voltage which is output by the respiratory gasconcentration detecting portion 100 on the basis of the receivingintensity of the standard referential light is indicated by V_(ref0),ref/ref0 can be approximated by V_(ref)/V_(ref0).

In the respiratory waveform analyzer 10 of the example, the reservedwater detecting portion 280 stores expression (Exp. 5) above, and thecomponents of expression (Exp. 5) above, i.e., the absorptioncoefficient (E), the concentration (C), and the voltage (V_(ref0))corresponding to the receiving intensity of the standard referentiallight are preset. In the example, the voltage (V_(ref0)) correspondingto the receiving intensity of the standard referential light may beobtained by actual measurement, or alternatively may be obtained, forexample, in the following manner on the basis of V_(ref) and the ratio(V_(sig)/V_(ref)) of V_(sig) and V_(ref).

FIG. 16 shows relationships between V_(ref) and V_(sig)/V_(ref) due to achange of the CO₂ concentration of the respiratory. Each of the plotsshown in FIG. 16 shows the relationship between V_(ref) andV_(sig)/V_(ref) at the CO₂ concentration indicated in the vicinity ofthe plot. The straight line shown in FIG. 16 shows a linearapproximation of the plots.

As shown in FIG. 16, the value of the voltage (V_(ref0)) correspondingto the receiving intensity of the referential light (standardreferential light) in a state where no water is reserved in therespiratory airway adaptor 20 can be approximately obtained by the valueof V_(ref) in the case where V_(sig)/V_(ref) is 1.0 on the straight lineobtained by the linear approximation of the plots (the value of V_(ref)at the plot indicated by “x” in FIG. 16).

FIG. 17 shows an example of waveforms of V_(sig), V_(ref), and the CO₂concentration which is generated on the basis of V_(sig), in the statewhere water is not reserved in the optical paths of the signal light andthe referential light inside the respiratory airway adaptor 20, and FIG.18 shows relationships between the waveforms of V_(sig) and V_(ref), andthe attenuance due to water which is reserved in the respiratory airwayadaptor 20, in the state.

FIG. 19 shows an example of waveforms of V_(sig), V_(ref), and the CO₂concentration which is generated on the basis of V_(sig), in the statewhere water is reserved in the optical paths of the signal light and thereferential light inside the respiratory airway adaptor 20, and FIG. 20shows relationships between the waveforms of V_(sig) and V_(ref), andthe attenuance due to water which is reserved in the respiratory airwayadaptor 20, in the state.

As shown in FIGS. 17 and 18, in the state, where water is not reservedin the optical paths of the signal light and the referential lightinside the respiratory airway adaptor 20, even when the voltage(V_(ref)) corresponding to the receiving intensity of the referentiallight, and the voltage (V_(sig)) corresponding to the receivingintensity of the signal light are varied by a change of theconcentration of CO₂ contained in the respiration of the subject, theattenuance (ECD in Exp. 5) is approximately 0.

As shown in FIGS. 19 and 20, by contrast, when water is reserved in therespiratory airway adaptor 20 to cover at least a part of the opticalpaths of the signal light and the referential light, both thereferential light and the signal light are attenuated. At this time, theattenuance (ECD in Exp. 5) is increased in accordance with the degreesof the attenuances of the referential light and the signal light.Therefore, the attenuance (ECD in Exp. 5) is more increased as thequantity of water reserved in the respiratory airway adaptor 20 islarger.

In the respiratory waveform analyzer 10 of the example, the reservedwater detecting portion 280 calculates the attenuance (ECD in Exp. 5)showing such a tendency, and, based on the value of the tendency, candetect the quantity of water reserved in the respiratory airway adaptor20. In the above described embodiment, the object for the detection isdescribed as the water. However, the respiratory waveform analyzer 10according to an aspect of the above embodiment can detect a material,for example a liquid, other than the water.

Although the invention has been described using the embodiment, thetechnical scope of the invention is not restricted to the scope of thedescription of the embodiment. It is obvious to those skilled in the artthat various changes or improvements can be made on the embodiment. Itis obvious from the definition of the appended claims that alsoembodiments in which such changes or improvements are made belong to thetechnical scope of the invention.

Although the respiratory waveform analyzer 10 is an apparatus formeasuring the CO₂ concentration in the respiration of the subject, forexample, the invention is not restricted to an apparatus for measuring aspecific component in the respiration of the subject. For example, anapparatus for measuring one or more components in the expiration orinspiration of the subject belongs to the technical scope of theinvention.

According to an aspect of the invention, when the concentration of acomponent in the respiratory gas of the subject is detected and therespiratory waveform on the basis of a temporal change of theconcentration is analyzed, the reliability of the respiratory waveformis referred, and therefore it is possible to correctly know noisecomponents in the respiratory waveform.

According to an aspect of the invention, when the effectiveconcentration of the component in each respiration cycle is detectedfrom the respiratory waveform, the use of the reliability causes a peakof noise components contained in the waveform corresponding to eachrespiration cycle, not to be falsely detected as the effectiveconcentration.

According to an aspect of the invention, when a value (average value)which is obtained by averaging effective concentrations of waveformscorresponding to respiration cycles is to be calculated, the averagingis performed after the effective concentrations are weighted inaccordance with the degree of the accumulated values of thereliabilities in the waveforms. Therefore, the effect of the noisecomponents contained in the waveforms against the calculated averagevalue (weighted average value) can be reduced.

According to an aspect of the invention, when the respiratory gas signalindicative of the concentration of the component has a specified valueor greater, the effective concentration detecting portion detects theeffective concentration during the concentration detecting time period.Therefore, the following effect is attained. Even in the case where,when the concentration of the component in the respiratory gas ismeasured by using the IR spectroscopy, water droplets or the like areattached to a light irradiation portion or detection portion for theexpiration, and the level of the output signal from the detectionportion is lowered, the detection is not affected by the level loweringof the output signal due to such an error cause, and hence it ispossible to detect more correctly the effective concentration.

According to an aspect of the invention, the apparatus includes theconcentration detection value correcting portion which corrects therespiratory waveform signal corresponding to the respiratory gas signal,in accordance with the ratio of the respiratory gas signal to thepredetermined reference value. Even when a measurement involving theerror cause is performed, therefore, an effect caused by the levellowering of the output signal can be reduced. Even in the case where theconcentration signal is largely varied in one respiration cycle by theerror cause, consequently, it is possible to prevent determination thata plurality of respirations are conducted, from being performed based onthe waveform (the respiratory waveform signal) due to the concentrationsignal. Further, since the apparatus includes the reserved waterdetecting portion, it is possible to detect the water in the respiratoryairway adaptor and to perform an attention arousal and an alarm to theuser of the apparatus.

What is claimed is:
 1. An expiratory waveform analyzer, operable toanalyze an expiratory waveform, which is generated based on aconcentration of a component in expiratory gas of a subject measuredover a plurality of time intervals, the expiratory waveform analyzercomprising: an expiratory gas concentration generator which generates aconcentration signal indicating values of the concentration of thecomponent based on an output signal from a sensor that measures theconcentration of the component; a flatness calculator which calculatesdifferences between the values of the concentration of the componentindicated by the concentration signal over the plurality of timeintervals of the expiratory waveform based on the concentration signal,and which calculates a flatness of the expiratory waveform based on thecalculated differences; a reliability calculator which calculates areliability of the expiratory waveform based on the flatness and thevalues of the concentration of the component indicated by theconcentration signal; and a respiratory rate detecting portion whichdetermines whether the expiratory waveform is reliable for inclusion incalculation of a respiratory rate of the subject based on thereliability of the expiratory waveform, and calculates the respiratoryrate of the subject using the expiratory waveform in response todetermining that the expiratory waveform is reliable and calculates therespiratory rate of the subject without inclusion of the expiratorywaveform in response to determining that the expiratory waveform is notreliable.
 2. The expiratory waveform analyzer according to claim 1,wherein the flatness is a function of an accumulated value which isobtained by accumulating differences between the concentration of thecomponent at time intervals during which the concentration of thecomponent generating the expiratory waveform is measured by the sensor,based on the concentration signal.
 3. The expiratory waveform analyzeraccording to claim 2, wherein the flatness is a function of absolutevalues of the differences.
 4. The expiratory waveform analyzer accordingto claim 2, wherein the flatness is equal to:$\frac{1}{\left\{ {{\Sigma\left( {D\;\Delta\; t\;{CO}\; 2} \right)}^{2} + 1} \right\}}$wherein DΔtCO2 is a difference between a current CO₂ concentration and aprevious CO₂ concentration at time interval Δt.
 5. The expiratorywaveform analyzer according to claim 1, wherein the reliabilitycalculator calculates the reliability based on the flatness which iscalculated at a timing by the flatness calculator, and the values of theconcentration of the component indicated by the concentration signal atthe timing.
 6. The expiratory waveform analyzer according to claim 5,further comprising: an effective concentration detector which detects avalue of the concentration signal at a timing when the reliability thatis calculated in a predetermined concentration detecting time period ismaximum, as an effective concentration of the component in theexpiratory gas in the concentration detecting time period.
 7. Theexpiratory waveform analyzer according to claim 6, wherein the effectiveconcentration detector accumulates the reliability in the concentrationdetecting time period to obtain an accumulated value in theconcentration detecting time period, determines whether the expiratorywaveform is reliable for inclusion in calculation of the effectiveconcentration of the component in the expiratory gas of the subjectbased on whether the reliability in the concentration detecting timeperiod exceeds a predetermined reliability, detects the effectiveconcentration in the concentration detecting time period in response todetermining that the expiratory waveform is reliable for inclusion incalculation of the effective concentration of the component in theexpiratory gas of the subject and does not detect the effectiveconcentration in the detecting time period in response to determiningthat the expiratory waveform is not reliable for inclusion incalculation of the effective concentration of the component in theexpiratory gas of the subject, and calculates the effectiveconcentration of the component in the expiratory gas of the subject,using the expiratory waveform if the expiratory waveform is reliable forinclusion in calculation of the effective concentration of the componentin the expiratory gas of the subject and calculates the effectiveconcentration of the component in the expiratory gas of the subjectwithout inclusion of the expiratory waveform if the expiratory waveformis not reliable for inclusion in calculation of the effectiveconcentration of the component in the expiratory gas of the subject. 8.The expiratory waveform analyzer according to claim 7, wherein theconcentration detecting time period is a time period corresponding toone cycle of the expiratory waveform.
 9. The expiratory waveformanalyzer according to claim 8, further comprising: a weighted averageprocessor which, when a plurality of the effective concentrations aredetected, weights each of the effective concentrations in accordancewith degree of the accumulated value in the corresponding concentrationdetecting time period, and averages the weighted effectiveconcentrations, to calculate a weighted average value.
 10. Theexpiratory waveform analyzer according to claim 9, further comprising: adisplay that displays at least one of a number at which the effectiveconcentration detector detects the effective concentration in a timeperiod, and the weighted average value calculated by the weightedaverage processor.
 11. The expiratory waveform analyzer according toclaim 6, wherein the expiratory gas concentration generator includes: anexpiratory gas concentration detector which converts an analog signaloutput from the sensor to a digital expiratory gas signal; and anexpiratory gas concentration calculator which generates the expiratorywaveform signal based on the expiratory gas signal from the expiratorygas concentration detector, the concentration signal is the expiratorywaveform signal, and when a value of the expiratory gas signal is avalue or greater, which indicates that the concentration of thecomponent is high, the effective concentration detector detects theeffective concentration in the concentration detecting time period. 12.The expiratory waveform analyzer according to claim 11, furthercomprising: a concentration detection value corrector which corrects theexpiratory waveform signal corresponding to the expiratory gas signal,in accordance with a ratio of the expiratory gas signal to apredetermined reference value.
 13. The expiratory waveform analyzeraccording to claim 1, further comprising: an expiratory airway adaptorin which the expiratory gas of the subject flows; and a liquid detectorwhich detects a liquid in the expiratory airway adaptor.
 14. Theexpiratory waveform analyzer of claim 1, wherein the reliability of theexpiratory waveform indicates one of (i) to include the expiratorywaveform in a determination of an expiratory rate of the subject and(ii) to ignore the expiratory waveform in the determination of theexpiratory rate of the subject.
 15. An expiratory waveform analyzercomprising: a sensor that detects over a duration of time aconcentration of a gas component of a subject at each of a plurality oftime intervals in the duration of time; an expiratory gas concentrationgenerator that generates an expiratory waveform over the duration oftime based on the concentration of the gas component at each of theplurality of time intervals; a flatness calculating portion thatcalculates differences between the concentration of the gas component ateach consecutive pair of the plurality of time intervals in the durationof time, and that calculates a flatness scaling factor for each of theplurality of time intervals based on the calculated differences; areliability calculating portion that scales the concentration of the gascomponent at each of the plurality of time intervals by the flatnessscaling factor for the respective each of the plurality of timeintervals, the scaled concentration of the gas component at each of theplurality of time intervals being a reliability of the concentration ofthe gas component at each of the plurality of time intervals; aneffective concentration detecting portion that determines a reliabilityof the expiratory waveform based on the reliabilities of theconcentration of the gas component at each of the plurality of timeintervals, compares the reliability of the expiratory waveform to awaveform reliability threshold, and determines whether the expiratorywaveform is a reliable expiratory waveform based on a result of thecomparing; and an expiratory rate detecting portion that calculates anexpiratory rate of the patient based on the expiratory waveform inresponse to the effective concentration detecting portion determiningthat the expiratory waveform is the reliable expiratory waveform,wherein the expiratory rate detecting portion calculates the expiratoryrate of the patient by ignoring the expiratory waveform in response tothe effective concentration detecting portion determining that theexpiratory waveform is not the reliable expiratory waveform.